Chromium Diffusion Coating on an ODS Ferritic-Martensitic Steel and Its Oxidation Behavior in Air and Steam Environments

A chromium diffusion coating was applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel to improve oxidation resistance at high temperature. By carrying out physical vapor deposition followed by inter-diffusion heat treatment, a thin Cr-rich carbide layer was produced on the ODS-FM steel. Both the as-received and surface-modified specimens were oxidation-tested at 650 °C in air and steam environments for 500 h. The surface-modified specimens showed improved oxidation resistance in both environments. In an air environment, both conditions exhibited a thin and continuous chromia layer, but the formation of Cr2O3 and (Mn, Cr)3O4 nodules resulted in greater weight gain for the as-received specimen. In a steam environment, weight gain increased for both the as-received and surface-modified specimen. Especially, the as-received specimen showed much greater weight gain with the formation of a thick oxide layer consisted of outer Fe-rich oxide and inner (Fe, Cr, Mn) oxide layers. On the other hand, a thin and continuous chromia layer was formed for the surface-modified specimen, which resulted in much less weight gain in a steam environment.

Oxidation and Hydrogen Behaviur in Zr-2Mn Alloy

The purpose of the present research was to determine the oxidation and hydrogenation behavior in the new Zr-2Mn alloy. The oxidation of alloy was performed at temperatures between 350°C and 900°C for 30 minutes. The hydrogen charging was made for 72 h at a current density 80 mA/cm2. The charged samples were heat treated at 400°C for 4 h to obtain a uniform hydrogen profile content across the sample. The oxidation resulted in an appearance of non-uniform oxide layers of thickness increasing with temperature. The surface damage was observed at higher temperatures 700 and 900°C. After charging with hydrogen followed by annealing no hydrides were found. The observed effect is evidence that the oxide layers may form effective barriers against hydrogen diffusion even if they are partially degraded. The absence of hydrides or hydride cracking may be caused by an absence in Zr-Mn alloys of such phase precipitates, which may trap diffusive hydrogen and initiate the hydrides. The positive influence of manganese on the formation of the thick oxide layer and relative resistance to delayed hydride cracking may be attributed to its affinity of oxygen, the ability to form thick and compact oxide layers during oxidation, the formation of solid solution in zirconium and no precipitates enhancing nucleation of hydrides.

Role of Copper Oxide Layer on Pool Boiling Performance With Femtosecond Laser Processed Surfaces

Copper pool boiling surfaces are tested for pool boiling enhancement due to femtosecond laser surface processing (FLSP). FLSP creates self-organized micro/nanostructures on metallic surfaces and creates highly wetting and wicking surfaces with permanent surface features. In this study two series of samples were created. The first series consists of three flat FLSP copper surfaces with varying microstructures and the second series is an open microchannel configuration with laser processing over the horizontal surfaces of the microchannels. These microchannels range in height from 125 microns to 380 microns. Each of these surfaces were tested for pool boiling performance. It was found that all the processed surfaces except one resulted in a decrease in critical heat flux and heat transfer coefficient compared to an unprocessed surface. It was found that the laser fluence parameter had a significant role in whether there was an increase in CHF or HTC. A cross sectioning technique was employed to study the different layers of the microstructure and to understand how FLSP could have a negative effect on the CHF and HTC. It was found that a thick oxide layer forms during the FLSP process of copper in an open-air atmosphere. The thickness and uniformity of the oxide layer is highly dependent on the laser fluence. A low fluence sample results in an inconsistent oxide layer of nonuniform thickness and subsequently an increase in CHF and HTC. A high laser fluence sample results in a uniformly thick oxide layer which increases the thermal resistance of the sample and allows for a premature CHF and decrease in HTC.

Auger and X-Ray Photoelectron Spectroscopy Study of the Tribocontact Surface after Laser Modification

The samples of the tool steel P6M5 were modified by means of laser irradiation (hereinafter - LO). The chemical composition of the sample surface before and after the LO was studied using the Auger and X-ray photoelectron spectroscopy (hereinafter - AES and XPS respectively). It was found that while the steel is exposed to LO, the thick oxide layer consisting mainly of the Fe2O3 oxide is formed. It was established that the modification with LO leads to increasing of wear resistance and durability of the R6M5 steel because of a double reduction of the friction coefficient.

Influence of Time on Thermal Oxidation of CP-Ti Grade II at 850 °C

The objective of this work is to understand the influence of time on thermal oxidation of CP-Ti Grade II at 850 oC. Thermal treatments were performed for 5 minutes, 15 minutes, 30 minutes, 60 minutes and 120 minutes of isothermal stage. The response of titanium to oxidation at same temperatures and various timings has been investigated, in terms of layer thickness, phase evolution. A variety of experimental and analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) and ball cratering test have been used to characterize the result of thermal oxidized surfaces. The results showed that oxygen diffused on Ti structure can produce a thick oxide layer with rutile (TiO2) between 3,50 and 10,34 microns, which exhibited good adhesion with the substrate.

600 V -Class V-Groove SiC MOSFETs

The authors applied a thick gate oxide layer at the trench bottoms to 600 V class truncated V-groove MOSFETs of which MOS channels were formed on 4H-SiC (0-33-8) facets and validated the static and switching characteristics. The specific on-resistance and the threshold voltage were 3.6 mΩ cm2(VGS=18 V,VDS=1 V) and about 1 V (normally-off), respectively. The breakdown voltage of the MOSFET with a thick oxide layer was 1,125 V (IDS=1 μA). The switching losses during turn-on and turn-off operations were estimated to be 105.8 μJ and 82.5 μJ (300 V, 10 A) at room temperature. The switching characteristics exhibited low temperature dependence for turn-on/off time.

4H-SiC Trench MOSFET with Thick Bottom Oxide

A 4H-SiC trench MOSFET has been developed that features trench gates with a thick oxide layer on the bottoms of the trenches. The maximum electric field strength and gate-drain charge of this device are 46% and 38%, respectively lower than that of a conventional MOSFET. The drain-source breakdown voltage is 1400V and the specific on-resistance is 4.4mΩcm2 at a gate bias of 20V and a drain voltage of 2V.

A Biocompatible SiC RF Antenna for In-Vivo Sensing Applications

ABSTRACTIn this study, we present a small-size implantable RF antenna (biosensor) which is made of fully biocompatible material, cubic silicon carbide. Silicon Carbide is one of the few semiconducting materials that combine biocompatibility and sensing potentiality. The hypothesis of a SiC based antenna, to be used for glucose monitoring, is that the changes in the medium surrounding the antenna affect the antenna properties such as input impedance and resonance frequency, and these changes can be used to estimate the patient’s plasma glucose level. An all-SiC patch antenna has been designed, simulated and fabricated with a target frequency of operation of 10 GHz. A Cu patch antenna was fabricated on SiC to serve as a reference antenna. The all-SiC antenna was realized by growing a poly-crystalline 3C-SiC film using CVD on a thick oxide layer that had been coated with poly-Si to serve as a growth template. A semi-insulating 4H-SiC substrate was used to minimize RF losses during operation.

Electrochemical Formation and Corrosion Properties of Porous TiOx Biomaterials

Formation of porous TiOx layers on Ti during electrochemical etching in H3PO4, CH3COOH electrolytes modified by HF and NH4F was described. The anodization resulted in porous TiOx formation, useful in tissue growth and bone bonding. The pore dimensions increased due to the increase of HF or NH4F content in H3PO4 electrolyte. During anodization at 10 V for 30 min, when the HF content increased from 0.5 to 10%, the pore diameter increased from 30 nm up to 8 m, respectively. Anodization in CH3COOH electrolyte resulted in non-uniform etching with flat hexagonal islands with nanopores inside surrounded by micropores. Corrosion properties of the etched samples were investigated in Ringer’s solution at 37oC and were compared to the unetched sample. The best corrosion resistance showed the samples etched at 10 V for 30 min in 1M H3PO4 + 2% HF and 1M H3PO4 + 10% NH4F, what can be attributed to thick oxide layer. We find, that porous sample presented good biocompatibility with human osteoblasts.

Microstructure of Surface and Subsurface Layers of a Ni-Ti Shape Memory Microwire

The microstructure of a 55 μm diameter, cold-worked Ni-Ti microwire is investigated by different transmission electron microscopy techniques. The surface consists of a few hundred nanometer thick oxide layer composed of TiO and TiO2with a small fraction of inhomogeneously distributed Ni. The interior of the wire has a core-shell structure with primarily B2 grains in the 1 μm thick shell, and heavily twinned B19′ martensite in the core. This core-shell structure can be explained by a concentration gradient of the alloying elements resulting in a structure separation due to the strong temperature dependence of the martensitic start temperature. Moreover, in between the B2 part of the metallic core-shell and the oxide layer, a Ni3Ti interfacial layer is detected.